150's have a heavier steering bolster, heavier front axle, and different steering. They have a larger fuel tank, different air cleaner, different sheet metal (to allow for larger fuel tank) The 150 has a higher capacity radiator. 150's came standard with flat top fenders (w/lighting), float ride seat, PAVT rear wheels, and full instrumentation. 150's due to front axle/steering bolster carried several hundred pounds more front weight, along with slightly longer wheel base, which made it more stable when carrying heavy weight on hitch.
At the time of their introduction in 1964, the 150 diesel was the most fuel efficient tractor tested by Univ of Nebraska.
Everything that's good about a 135 is just a little BETTER on a 150! I've got two of them. One, a 1971 model, I've owned since new.